In mass spectrometry, a sample is ionized and the ions are separated according to mass (more accurately, according to mass-charge ratio), and an intensity signal corresponding to the number of ions is measured. The measurement results, in which mass is shown on the horizontal axis and signal intensity (generally, relative intensity) on the vertical axis, constitute a mass spectrum.
If the sample molecules have a large molecular weight and a complex structure, sometimes ions of a specified mass are selected as precursor ions (parent ions), and the selected precursor ions are cleaved by CID (collision induced dissociation). The fragment ions produced by cleavage are separated according to mass in the same manner as above, and a mass spectrum based on the fragment ions is generated. This cleavage operation may be performed multiple times, in which case a mass spectrum is acquired at each stage of cleavage. A mass spectrum obtained by repeating the cleavage operation (n−1) times (where n is an integer equal to or greater than 2) is commonly referred to as an “MSn spectrum.”
To analyze a mass spectrum, there is the method of using a mass spectrum library (database). A mass spectrum library includes information on various known compounds, i.e. mass spectrum data obtained when performing mass spectrometry using a predetermined ionization method, as well as information such as compound name, molecular weight, composition formula, structural formula, etc. These mass spectra of known compounds and the measured mass spectrum obtained through measurement are subjected to pattern matching under designated search parameters, and information on known compounds similar to the peak pattern of the measured mass spectrum is obtained.
It is desirable for the information obtained from a mass spectrum library, etc. to be displayed on a screen together with the mass spectrum so as to be easy to understand by the user. A simple display method of this sort includes the method of displaying the mass at the top of all peaks or of representative peaks. Furthermore, although different from mass spectrometry, Patent literature 1 describes a method whereby, when a user moves the cursor of a pointing device such as a mouse over a graph displayed on a screen, numerical values or other detailed information is displayed at the cursor location. Applying the method of Patent literature 1, as shown in FIG. 6, there is the method of displaying peak information (in the drawing, structural formula candidates) for peaks of the mass spectrum designated by the user based on the cursor location.